This invention generally relates to methods and apparatus for detecting innovations, such as changes or movement, in a scene or view, and more particularly, to using associative memory formalisms to detect such innovations.
In many situations, an observer is only interested in detecting or tracking changes in a scene, without having any special interest, at least initially, in learning exactly what that change is. For example, there may be an area in which under certain circumstances, no one should be, and an observer may monitor that area to detect any movement in or across that area. At least initially, that observer is not interested in learning what is moving across that area, but only in the fact that there is such movement in an area where there should be none.
Various automatic or semiautomatic techniques or procedures may be employed to perform this monitoring. For instance, pictures of the area may be taken continuously and compared to a "standard picture," and any differences between the taken pictures and that standard picture indicate a change of some sort in the area. Alternatively, one could subtract adjacent frames of a time sequence of pictures taken of the same scene in order to observe gray level changes. It is assumed herein that the sampling rate, i.e. the frame rate, is selected fast enough to capture any sudden change or motion (i.e. "innovations" or "novelty"). This mechanization would not require knowledge of a "standard picture". More particularly, each picture may be divided into a very large number of very small areas (picture elements) referred to as pixels, and each pixel of each taken picture may be compared to the corresponding pixel of the standard or adjacent frame picture. The division of a picture containing the scene into a larger number of pixels can be accomplished by a flying spot scanner or by an array of photodetectors/photosensors as well known to those versed in the art. The resultant light intensity of the discretized picture or image of the scene can be left as analog currents or voltages or can be digitized into a number of intensity levels if desired. We will refer to the photodetector/photosensor output current or voltage signal as the input signal to the apparatus described herein. Whether the input signal is a current or voltage depends on the source impedance of the photodetector/photosensor as well known to those versed in the art. This may be done, for example, by using photosensors to generate currents (or voltages) proportional to the amount of light incident on the pixels, and comparing these currents to currents generated in a similar fashion from the amount of light incident on the pixels of the standard scene. These comparisons may be done electronically, allowing a relatively rapid comparison. Even so, the very large number of required comparisons is quite large, even for a relatively small scene. Because of this, these standard techniques require a very large amount of memory and are still comparatively slow. Furthermore, changes in the scene can be caused not only by gray level differences but also by innovations or novelty (changes) in the texture of the scene. In such cases the method of reference comparisons or subtracting adjacent frames would not work. Hence, these prior art arrangements do not effectively detect changes in the texture of a scene.